Luidiidae Family of Starfish

Phylogeny: Luidiid Sea Stars of the Luidiidae Family are in the phylum Echinodermata, which is a large Phylum that includes brittle stars, sea cucumbers, sea lilies, sea stars and sea urchins. The Echinodermata are of great scientific interest because, via fossil records, they have been dated to the Cambrian Age (over 500,000,000 years ago) with 7,000 living and 13,000 extinct individual species. The Luidiidae Family is in the subphylum Asterozoa and the class Asteroidea.  Asteroideans are easily distinguished from Ophiuroideans as their arms have a broad attachment point where the arms join the disk and taper as they extend from the disk. Ophiuroideans have arms that are relatively the same thickness their entire length, giving them a narrow attachment point at the disc. Luidiid Sea Stars are in the subclass Ambuloasteroidea, the infraclass Neoasteroidea, the superorder Valvatacea, and the order Paxillosida. The Paxillosida order is characterized by having only one larval phase, compared to the two phases of other orders in this class.  The Luidiidae Family is one of eight families in this order. The genus Luidia is the only genus in the Luidiidae Family and there are around fifty species in this genus. The family and genus names are in honor of the Welsh naturalist and botanist Edward Lhuyd, who Latinized his name to Luidius.

Morphology:  Luidiid Sea Stars are characterized by having only one larval phase, compared to the two phases of other orders within this class. At the adult stage they have 5-rayed radial symmetry. They have an unsegmented, small, flattened, flexible, central disk, which is covered with skin. The arms have a broad attachment point where they join the disk, and they taper toward their end. They have  large mouth angle plates comprised of fused ambulacral ossicles. They lack an anus, and are unable to extrude their stomach like most other sea stars. They have sessile pedicellariae. Their tube feet are pointed and  are used, along with their spines, to borrow under the surface of soft sediments. They have a unique water-vascular system that uses hydraulic power to operate a multitude of tube feet that are used in locomotion and food capture. Their tube feet lack suckers, but have double ampullae (bulb-like appendages that push water into tube feet, causing them to extend). The pedicellariae may be either stalked or sessile. They have a complete digestive system, but they lack a head, eyes, nervous system, or excretory system. The disk contains most of the organs, with the mouth on the ventral side and the anus and madreporite (entry plate for the water vascular system) on the dorsal surface. While most sea stars, to avoid predation, can automize (self-amputate) their arms, where the arm joins the disk,  Luidiidae Sea Stars can do so at any point along the arm. They have the ability to regenerate amputated limbs. Sea Stars in the Luidiidae Family are often brightly colored. Luidiids reach up to 60 cm (23 inches) in diameter.

Habitat and Distribution:  Luidiid Sea Stars are found on sand, mud, and muddy gravel substrates. They live from the intertidal zone to depths up to 1,300 m (4,260 feet). They are found worldwide in tropical to temperate seas. At least eleven species from this family are found in Mexican waters.

Reproduction: Most Luidiidae species are gonochoric (male or female for life). They reproduce sexually, through broadcast spawning, with external fertilization. The eggs hatch into planktonic larvae before settling to the bottom to metamorphose into juvenile sea stars.

Ecosystem Roles:  Luidiid Sea Stars may be scavengers that eat carrion and detritus, or they may be predators that eat bivalves, crustaceans, gastropods, polychaetes, sea cucumbers, sea urchins, and other sea stars. In turn Luidiids are preyed upon by shore-birds, crabs, fish, and other sea stars.